System and method of cooling

ABSTRACT

The invention provides a cooling fluid heat exchange unit including: a primary heat exchange unit including a closed circuit for circulation primary circuit fluid; and a secondary heat unit adapted to provide cooled air in communication with the primary heat exchange unit. The closed circuit for the cooling fluid as it passes through the primary heat exchange unit ensures that the cooling fluid is prevented from exposure to the atmosphere, and in particular, to the air forced through the heat exchange unit.

FIELD OF THE INVENTION

The system and method of the present invention relates generally to thecooling of air and more particularly to a system and method of coolingair in systems including a heat exchange unit to effect heat transferfrom a cooling fluid. The invention is particularly suited to coolingsystems for relatively large volumes which is required in circumstancessuch as the cooling of air in large office buildings.

BACKGROUND OF THE INVENTION

Areas occupied by people generally require some form of heating and/orcooling in order to maintain the area at a reasonable temperature. Insome instances, statutory or contractual arrangements require an area orpremises to be maintained within certain temperature limits.

Accordingly, heating and cooling systems have developed over time andexist in most modern premises in order to maintain the temperature inthose premises within predetermined temperature limits.

Heating and cooling large areas such as office buildings usuallyrequires a significant capital investment in the plant and equipmentthat effects the heating and/or cooling.

In warm climates, cooling systems incorporating a cooling tower havebecome a popular type of system for the cooling of large buildings. Inthis type of system, a refrigerant gas is used to cool air as it passesthrough a first heat exchange unit (evaporator) and having absorbedenergy from the air, the refrigerant gas is passed to a second heatexchange unit (condenser) wherein heat is extracted from the refrigerantgas. The second heat exchange unit is supplied with water to effectcooling of the refrigerant gas and having absorbed energy, the water isgenerally transferred to a third heat exchange unit (cooling tower) inorder to cool the water in preparation for further use. Whilst this typeof system is commonly used for large office buildings, cooling towersunfortunately provide an environment conducive to the generation anddistribution of a bacterium known as legionella pneumophilia. Thebacterium becomes airborne and subsequent inhalation by people in thevicinity of a cooling tower may lead to the development of a diseasecommonly referred to Legionnaires' Disease.

The bacterium was first identified in Philadelphia, USA in July 1976 andsince that time, infection in both sporadic and epidemic forms hasoccurred in Australia and many overseas countries. Epidemiologicalinvestigations have generally failed to identify the precise source ofinfection, however, cooling towers and water distribution systems aregenerally recognised as the most likely source. Legionnaires' Diseasetypically manifests itself as severe pneumonia with patients presentingearly symptoms of malaise, muscle pains, headache and fever. Patientsbecome increasingly short of breath and the respiratory symptomsprogress to pneumonia, often culminating in respiratory failure. Thedevelopment of Legionnaires' Disease is usually associated with mentalconfusion and delirium, vomiting and renal failure. The diseasegenerally has an incubation period of 2 to 10 days and whilst thefatality rate from confirmed Legionnaires' Disease in Australia hasdecreased over the past six years, fatalities still occur. Legionnaires'Disease was proclaimed a Notifiable Disease in Australia in 1979 and allcases must be notified by health professionals to the relevant HeathDepartment upon detection.

Having recognised the propensity for cooling towers to generate anddistribute the legionella pneumophilia bacterium, various approacheshave been implemented to minimise the likelihood that a tower can formand distribute the bacterium. In particular, treatment of cooling towerwater with corrosion inhibitors, surfactants, biocides and otherchemicals is frequently proposed in order to reduce microbial growth.

Generally, a broad spectrum biocide is recommended for the watertreatment process in order to reduce total microbial load in coolingtower water. However, in the dynamic environment of a cooling towersystem, the performance of chemicals is different from that incontrolled laboratory trials. For example, cooling tower water issubjected to temperature changes and varying flow velocities atdifferent locations in the system. Many other parameters including pHlevel, conductivity, total dissolved solids, suspended matter and thebiological mass within the system can also vary over time.

As a result, the efficacy of water treatment with a broad spectrumbiocide cannot be predetermined for any particular environment and assuch, ongoing sampling of cooling tower water is required to ensure thatmicrobial growth has been limited to an acceptable level in addition toany chemical treatment. Apart from the cost of the biocides, therequirement for ongoing sampling has the effect of significantlyincreasing the maintenance cost for a cooling tower system.

The use of ozone has also been proposed and has been successfully usedin some instances to reduce microbial growth. Although ozone is anunstable chemical, it is a powerful oxidising biocide and must beproduced on-site by means of an ozone generator and used immediately forwater treatment. Ozone disinfection is relatively new for the control ofbacterial levels in cooling tower waters and it is generally recognisedthat care must be exercised to maintain the generators in accordancewith manufacturers' recommendations thus ensuring optimum efficiency.Apart from the significant capital investment required for an ozonegenerator, there remains some doubt as to the efficacy of this type ofsystem for preventing microbial growth and the spread of Legionnaires'Disease.

The use of ultraviolet light has also been proposed for the reduction ofbacterial levels in cooling tower water. With these types of systems,the cooling tower water is exposed to ultraviolet radiation of asufficient intensity to eliminate bacterium in the water. It isimportant to ensure that the water is exposed to a sufficient level ofultraviolet radiation intensity for the system to be effective. Sensorsare generally used to monitor the intensity of the ultraviolet radiationand any reduction in efficacy as detected by the sensors generallyprovides an indication that maintenance is required. Ultravioletradiation has no effect on the pH, odour or chemical composition ofcooling tower water. However, the colour, tepidity and chemicalcomposition of the water can interfere with ultraviolet radiationtransmission and as such, determination of the ultraviolet absorbency ofthe water to be treated prior to installing ultraviolet equipment isusually advisable. Bacteria may be protected by tepidity, clumping orthe presence of slime and accordingly, appropriate water filtration isusually recommended in conjunction with ultraviolet radiation systems.

Despite implementing such a system to destroy bacterium, the ultravioletdamage to bacterium can be significantly reversed by enzyme repairmechanisms such as those which operate in darkness and on subsequentexposure to bright light (photoreactivation). Once again, theinstallation of an ultraviolet radiation system involves a significantcapital expenditure and is not an attractive option given that theefficacy of these systems is still currently questionable.

Various other proprietary devices have been proposed for the treatmentof water including systems that expose the treated water toelectromagnetic and electrostatic fields. There is a lack of conclusivescientific evidence to demonstrate that these proprietary devices haveany significant effect on the microbial load in treated water. Survivaland growth of the legionella bacteria in controlled laboratory fieldtrials is currently being conducted for these systems.

Whilst filtration systems present the simplest method available for thereduction of microbial matter in water, a full-flow filtration plantthat will remove fine particles is generally not practicable for mostexisting systems due to space and weight restrictions. Additionally,such filtration systems have associated installation and operationalcosts that generally render this approach economically infeasible. Inany event, with any type of filtration system, there is necessarily anongoing maintenance cost for backflushing and replacement of filters.

Irrespective of the water treatment systems currently in use, ongoingmaintenance in the form of water sampling cannot be avoided andnecessarily increases the ongoing maintenance cost for the operation ofa cooling system incorporating a cooling tower.

Accordingly, it is an object of the present invention to provide acooling system and method of cooling for systems that, under normalworking conditions, eliminates the possibility of the cooling systemgenerating airborne bacterium known as legionella pneumophilia.

A secondary object of the invention is to provide a cooling system andmethod of cooling for systems that enables existing cooling systems thatcould generate airborne bacterium known as legionella pneumophilia to bemodified to eliminate any possibility of the system, under normalworking conditions, generating such airborne bacterium.

Any discussion of documents, act, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in Australia inthe field relevant to the present invention as it existed before thepriority date of each claim of this application.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a cooling fluid heatexchange unit including:

-   -   a primary heat exchange unit including a closed circuit for        cooling fluid;    -   an air cooler located upstream of the primary heat exchange        unit; and    -   a fan arrangement operable to force air through the cooler and        the primary heat exchange unit,    -   wherein said air cooler includes a moisture absorbent material        that is, in use, maintained moist such that air forced through        the cooler is cooled by the action of evaporation prior to being        forced over a portion of the closed circuit in the primary heat        exchange unit.

The closed circuit for the cooling fluid as it passes through theprimary heat exchange unit ensures that the cooling fluid is preventedfrom exposure to the atmosphere, and in particular, to the air forcedthrough the heat exchange unit. This separation removes the risk of thegeneration and distribution of the legionella bacterium. In practice,the closed circuit is likely to form part of a loop within a coolingsystem where the cooling fluid is transported from a location where thefluid is used to absorb thermal energy and subsequently transported tothe heat exchange unit in order for the cooling fluid to release theabsorbed thermal energy.

In a preferred embodiment, the cooled air emitted from the air cooler issubstantially free of fluid in a liquid state. In a particularlypreferred embodiment, the air cooler and the primary heat exchange unitare separated by a distance along the path of air flow from the coolerto the primary heat exchange unit to reduce the likelihood of fluid in aliquid state passing from the air cooler and impinging upon the primaryheat exchange unit.

Preferably, the heat exchange unit includes a plurality of air inletsand outlets with the fan arrangement disposed therebetween and operableto draw air in through the plurality of inlets and force air out throughthe plurality of outlets. The air cooler may be located over theplurality of air inlets such that air drawn through the air cooler bythe fan arrangement is cooled prior to being drawn or forced over theprimary heat exchanger and subsequently through the plurality of airoutlets.

Where the cooling fluid is water, the cooling water preferably passesthrough the primary heat exchanger in thermally conductive tubing, suchas copper tubing, with drawn air passing over the tubing and removingthermal energy from the water passing through that tubing.

The air cooler preferably includes a water absorbent material similar tothat used in evaporative cooling applications and may include wood fibreor cooling pad material such as that distributed under the trade mark“CELDEK”. The moistened water absorbent material cools air passingthrough the material by the action of evaporation. This effect is usedgenerally in evaporative cooling systems and water, separate from thecooling fluid, may be supplied to the water absorbent material usingapparatus similar to that in current evaporative cooling systems.

The use of water for the air cooler that is separate to the coolingwater passed through the primary heat exchanger does not pose any riskof generating or distributing the legionella bacterium as the air coolerwater temperature does not rise to a sufficient temperature to presentsuch a risk.

Generally, pads of water absorbent material would be locatedsubstantially vertically over the air inlets of the heat exchange unitand water would be applied to an upper portion of the water absorbentpads and would migrate through and moisten the entire pad. In the eventthat water is applied to the absorbent material paid at a rate fasterthan evaporation therefrom, a holding tank may be suspended below thematerial pads in order to collect water run-off. Any water run-offcollected in a tank may be reused by pumping that water back to theupper portion of the material pads for reapplication thereto.

In a particularly preferred embodiment, a water absorbent material padincluding a plurality of fluted apertures of a size less than 7 mm isused as part of the air cooler. Ordinarily in evaporative coolingapplications, a water absorbent material pad with a plurality of 7 mmfluted apertures is used. However, in this embodiment of the invention,use of a pad with fluted apertures of a size less than the standard sizeof 7 mm has been found to provide a more efficient cooling effect. Thisparticular embodiment also uses variable pitch fans for drawing airthrough the primary heat exchanger and through the air cooler pads. As aresult of the increased efficiency resulting from the use of a pad withfluted apertures less than 7 mm, the overall pad size may be reducedwhilst still achieving the same cooling effect that of a pad withstandard sized fluted apertures. A reduction in the overall size of anair cooler pad may be significant for installations where a conversionfrom an existing cooling tower arrangement is required and there islimited physical space in which to install a new cooling fluid heatexchange unit.

In another embodiment, the cooling fluid comprises highly concentratedammonia with a primary heat exchange unit comprising stainless steel oraluminium tubing effecting passage of the ammonia through the heatexchange unit. In this particular embodiment, the ammonia enters theprimary heat exchange unit in a gaseous state and upon having thermalenergy removed, the ammonia is emitted in a liquid state. Whilst ammoniahas previously been used as a cooling fluid, it has only been feasiblefor extremely large installations. As a result of the improved coolingefficiency from use of an air cooling stage, an effective andeconomically feasible cooling fluid heat exchange unit using ammonia asthe cooling fluid may be produced for smaller installations.

In another aspect, the present invention provides a method of coolingfluid in a cooling fluid heat exchange unit, the method including thesteps of:

-   -   passing cooling fluid of a cooling system through a primary heat        exchanger having a closed fluid circuit such that the cooling        fluid is contained;    -   placing an air cooler upstream of the primary heat exchanger;        and    -   causing a flow of air through the air cooler and over a portion        of the closed fluid circuit wherein said air cooler includes a        moisture absorbent material that is, in use, maintained moist        such that the air is cooled by vaporising fluid.

In a particularly preferred embodiment, the cooling fluid heat exchangeunit of the present invention is manufactured in a range of heatexchanging capacities such that a heat exchanger according to thepresent invention may be used to replace an existing cooling tower of asimilar heat exchanging capacity.

In yet another aspect, the present invention provides a method ofconverting a cooling system incorporating a first heat exchange unitincluding a fluid cooling heat exchange unit where the fluid is exposedto air drawn through the heat exchange unit by replacing said first heatexchange unit with a second heat exchange unit including a primary heatexchanger and an air cooler including a moisture absorbent material thatis, in use, maintained moist such that air forced through the air cooleris cooled by the action of vaporisation where the fluid in the primaryheat exchange unit is contained and prevented from exposure to airforced through the air cooler and then subsequently passed through thesecond heat exchange unit, the method including of steps of:

-   -   disconnecting the first heat exchange unit cooling fluid inlet        and outlet connection;    -   reconnecting the fluid inlet and outlet to the corresponding        connection points of the second heat exchange unit; and    -   operating the cooling system.

In most conversions, it is likely that the first heat exchange unit willbe removed to provide room for the second heat exchange unit although itis not essential.

In a further aspect, the present invention provides a cooling systemhaving a fluid cooling heat exchange unit including:

-   -   a primary heat exchange unit including a closed circuit for        cooling fluid;    -   an air cooler including a moisture absorbent material that is        maintained moist for cooling air by evaporation said air cooler        located upstream of said primary heat exchange unit; and    -   a fan arrangement operable to force air through said air cooler        and said primary heat exchange unit,    -   wherein air forced through said air cooler is cooled prior to        being forced over a portion of said closed circuit in said        primary heat exchange unit.

In yet a further aspect, the present invention provides a cooling systemhaving a fluid cooling heat exchange unit including:

-   -   a primary heat exchange unit including a closed circuit for        circulating fluid; and    -   a secondary heat exchange unit including a moisture absorbent        material that is, in use, maintained moist, the secondary heat        exchange unit adapted to provide air cooled by the action of        evaporation in communication with said primary heat exchange        unit.

Throughout this specification the word “comprise” or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating the main components of aconventional cooling system including a heat exchange unit in the formof a cooling tower;

FIG. 2 is a schematic diagram illustrating the main components of acooling system incorporating an air-cooled condenser;

FIG. 3 is a schematic diagram illustrating a cooling systemincorporating a heat exchanger according to an embodiment of the presentinvention; and

FIGS. 4A and 4B are a side and sectional side view respectively of theheat exchange unit of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a schematic diagram of a conventional coolingsystem incorporating a cooling tower is provided. This type of system iscommon for large buildings that have a relatively large space to cooland are usually arranged such that the majority of the cooling system islocated in the basement of the building with a cooling tower situated onthe roof of that building.

In FIG. 1, a building 10 has an installed cooling system comprising arefrigerant gas circuit 12 passing through a condenser 14 and anevaporator 16. The flow of refrigerant gas through the circuit 12 isdriven by a compressor 18 and regulated by expansion valve 20. Air inthe building 10 is generally cooled by drawing air through a duct inwhich a portion of the chilled water circuit 22 that effects cooling ofair in the building 10 is not detailed herein.

Refrigerant gas is passed through the condenser 14 for the purpose ofcooling the refrigerant gas. Generally, in large buildings, therefrigerant gas is cooled by the use of water. Subsequent to absorbingthermal energy from the refrigerant gas in the condenser 14, the wateris transferred to a cooling tower 26 by way of a pump 24. As previouslydescribed, it is usual for cooling towers to be placed upon the roof ofa building 10 as cooling towers are usually large and emit a substantialamount of noise during operation.

Hot water from the condenser 14 travels via pipe 28 to the water inletof the cooling tower 26. The cooling tower 26 then extracts thermalenergy from the water and cold water is drawn from the cooling tower 26through pipe 30.

Cooling towers generally effect the removal of heat from cooling waterby use of air flowing through the cooling tower to effect evaporation ofa portion of the water. To evaporate some of the water, thus causing thewater to transfer from a liquid to a gaseous state, thermal energy isrequired and this is extracted from the remaining water that continuesto remain in a liquid state. Accordingly, as thermal energy is removed,the temperature of the water in the tower decreases.

The most commonly used form of cooling tower uses induced draughtcounter-flow where air is drawn through the tower by a fan located atthe discharge of the cooling tower. Air enters the tower through louvresand is drawn vertically through the tower in a direction opposite to theflow of cooling water through the tower. Another type of cooling towerhas a fan mounted on one side of the tower with air either forced orinduced through the tower in a cross-flow manner past falling water. Inany event, all known types of cooling towers involve the exposure ofcooling water to air drawn or forced through the tower and the storageof water in a basin for a period of time prior to that cooled waterbeing drawn by the pump 24 through piping 30. This type of arrangementis common as it is relatively inexpensive to use a fluid such as waterto effect heat exchange and to pump that water to a roof top mountedheat exchanger in order to cool the water.

FIG. 2 illustrates an alternative conventional cooling systemarrangement wherein the system comprises an enclosed loop of refrigerantgas 40 which is compressed by means of a compressor 42. The refrigerantgas is passed through an evaporator 46 where it absorbs thermal energyfrom a water circuit 40. The cooling of air in the building 35 occurs ina similar manner as for the system described in FIG. 1. However, incontrast to the system of FIG. 1, the system illustrated in FIG. 2 doesnot include a water cooled condenser and cooling tower arrangement forthe purpose of removing thermal energy from the refrigerant gas.Instead, refrigerant gas is pumped from the basement of the building 35up to the rooftop of the building and passed through an air cooledcondenser 45. The air cooled condenser 45 includes electrically drivenfans (47 and 49) for the purpose of drawing air through the air cooledcondenser via air inlets and expelling the drawn air through airoutlets.

Generally, refrigerant gas is contained in thermally conductive pipingthat is formed in a tortuous path which resides within a region of theair cooled condenser 45 and is subject to airflow.

The type of cooling system illustrated in FIG. 2 is usually used ininstallations where the distance between the plant room and the aircooled condenser is sufficiently short to do so. If the distance is toolong for it to be feasible to transfer gas, then alternative arrangementis sought. In most instances where a heat exchange unit will be mountedon the roof top of a building, the distance from the plant room to theheat exchange unit is sufficiently long to render this type of systeminfeasible.

An embodiment of the present invention is illustrated in FIG. 3 whereina cooling system for a building 50 includes an enclosed circuit ofrefrigerant gas 52 that is passed through a condenser 54 and anevaporator 56 by a compressor 58. The flow of gas through the enclosedcircuit 52 is controlled by an expansion valve 60. The evaporatorincludes an enclosed water circuit 62 which has thermal energy removedtherefrom in order for the enclosed water circuit 62 to be used toeffect cooling of the air in the building 50 in a similar manner asdescribed previously (refer FIG. 1). As for the system illustrated inFIG. 1, the condenser 54 operates as a heat exchanger to extract thermalenergy from the enclosed loop of refrigerant gas 52.

The removal of thermal energy from the enclosed loop of refrigerant gas52 in the condenser 54 is effected by the use of another fluid, usuallywater, which is drawn into the condenser 54 through piping 66 andcarried out of the condenser 54 through piping 68. Cooling water isdrawn into the condenser 54 and passed through it under the control ofpump 70. Water emitted from the condenser 54 is carried by piping 68 tothe rooftop of the building 50 where it enters a rooftop mounted heatexchanger 75.

The heat exchanger 75 includes electrically driven fans (77 and 79) thatoperate to draw air therethrough. The piping 68 is generally thermallyconductive and formed in a tortuous path with that portion formed in atortuous path disposed in a region that will be subject to air flow asair is drawn through the heat exchanger 75. Along the portion of thepiping that is formed in a tortuous path, thermally conductiveextensions may be connected to the piping 68 in order to improve theefficiency of removing thermal energy from the water in the piping 68 asair passes over the piping 68 and the thermally conductive extensions.Usually, thermally conductive extensions comprise heat fins formed froma suitably thermally conductive material. Having passed through theportion of piping formed in a tortuous path, the water is then carriedout of the rooftop mounted heat exchanger 75 via piping 66 and is onceagain pumped into the condenser 54 by action of the pump 70.

In addition to passing cooling water through a portion of piping subjectto forced airflow, the rooftop mounted heat exchanger 75 also includesmoistened water absorbent material suspended over the air inlets of theheat exchangers 75 such that air drawn through the moistened waterabsorbent material is cooled by the action of evaporation prior to thatair passing over the portion of piping 68 formed in a tortuous path. Asa result of cooling air prior to passing it over piping carrying wateremitted from the condenser 54, the effectiveness of removing thermalenergy from that fluid is significantly increased.

A side view and a sectioned view of the heat exchanger 75 are providedin FIGS. 4A and 4B respectively.

With reference to FIG. 4B, the heat exchanger 75 includes electricallydriven fans (77 and 79) arranged to draw air through the heat exchangers75. The side walls of the heat exchanger (82 and 84) comprise thermallyconductive piping formed in a tortuous path carrying water from thecondenser 54 the piping residing in a region subject to air flow throughthe heat exchanger 75. The thermally conductive piping is wound througha tortuous path to extend substantially over the entire region subjectto airflow and in the sectional view of FIG. 4B, the piping extendssubstantially perpendicularly into and out of the plane of the diagram.

In the embodiment of the heat exchanger 75 as detailed in FIG. 4B, theside walls 82 and 84 effectively form two banks of the heat exchangers,each acting to remove thermal energy from the water passingtherethrough. In this respect, water enters the heat exchange banks 82and 84 through inlets 68 and 68 a and having passed through therespective heat exchange banks are emitted therefrom throughcorresponding outlets 66 and 66 a. Water enters the heat exchange banks82 and 84 through inlets 68 and 68 a in a “hot” state and having hadthermal energy extracted therefrom, the water is emitted from the heatexchange banks 82 and 84 through outlets 66 and 66 a in a “cold” state.Of course, the inlets, 68 and 68 a, may be connected by a common header.Similarly, the outlets, 66 and 66 a, may also be connected to a commonheader.

Whilst thermal energy would be extracted from water passing through theheat exchange banks 82 and 84 solely by action of air drawn throughthose heat exchange banks, the efficiency of the extraction of thermalenergy from water passing through the heat exchange unit issignificantly improved by suspending moistened water absorbent materialover the air inlets of the heat exchanger 75.

With reference to FIG. 4B, water absorbent material pads 85 and 87 aresuspended over the air inlets of the heat exchanger 75 such that airpassing over the heat exchange banks 82 and 84 is required to passthrough the water-absorbent material pads 85 and 87 first.

In a preferred embodiment, the water absorbent material pads 85 and 87comprise material distributed under the trademark “Celdek” and thesepads 85 and 87 are continually moistened by the application of water tothe top of each of the pads 85 and 87 at inlets 90 and 92. Water appliedat inlets 90 and 92 eventually trickles down through the water absorbentmaterial pads 85 and 87 substantially wetting the entire material pad.In the event that the material pads 85 and 87 do not fully absorb waterapplied to the inlets 90 and 92, run-off from the bottom of each pad maybe collected in a tank (not detailed herein) that may be returned to thewater inlets 90 and 92 via a pump (also not detailed).

Air drawn through the material pads 85 and 87 is cooled by the action ofevaporation and the passing of this cooled air over the heat exchangebanks 82 and 84 acts to significantly increase the efficiency of theextraction of thermal energy from water passing through those heatexchange banks.

In a particularly preferred embodiment, a water absorbent material padcomprising a plurality of fluted apertures of a size less than 7 mm indiameter is used as part of the air cooler. Additionally, in thisembodiment, variable pitch fans are used to draw air through the primaryheat exchanger and the air cooler pads. The use of a water absorbentmaterial pad with apertures of a diameter less than the standarddiameter results in a more efficient air cooling effect and as such, theoverall size of the water absorbent material pad may be reduced whilststill providing a similar cooling effect as a pad with larger apertures.A reduction in overall pad size may be critical for installations wherethe heat exchange unit must conform to physical space restrictions. Inthese instances, a reduced overall pad size may result in a heatexchange unit according to the present invention being a feasible optionfor that particular installation.

In a further embodiment, the cooling fluid comprises highly concentratedammonia with a primary heat exchange unit comprising stainless steel oraluminium tubing effecting passage of the ammonia through the heatexchange unit. Whilst ammonia has previously been used as a coolingfluid, it has generally been restricted for use in very largeinstallations. However, the improved cooling effect of a heat exchangeunit according to the present invention enables the construction of aheat exchange unit comprising an ammonia cooling fluid of a reducedphysical size with a similar cooling capacity as that for a larger sizedconventional heat exchange unit. As a result, heat exchange units usingammonia as the cooling fluid become a more economically feasible optionfor relatively small installations.

The present invention embodies many advantages, the most significant ofwhich being the provision of an alternative heat exchange unit that doesnot present a risk of generating and distributing airborne legionellabacterium that may be used to replace existing cooling tower heatexchange units. In this respect, whilst many approaches have beenproposed for over coming the disadvantages of cooling towers and theirsusceptibility to generate and distribute the legionella bacterium, mostof these approaches involve a substantial increase to the ongoingmaintenance cost of the cooling system.

In contrast to most prior proposals, the current invention maintainscooling fluid in an entirely enclosed circuit such that the coolingfluid is not exposed to the environment. As such, the possibility of thecooling fluid distributing legionella bacterium into the environment ina system according to the present invention and under normal workingconditions is completely eliminated.

Additionally, the arrangement of the current invention lends itselfparticularly well to the replacement of existing cooling towerarrangements by maintaining the use of a condenser in the basement of abuilding and the pumping of cooling fluid to a rooftop heat exchanger.In particular, the conversion of an existing cooling system arrangementincorporating a cooling tower to a system according to the presentinvention is relatively easily effected by the disconnection of waterinlet and outlet conduits from the existing cooling tower, removal ofthe cooling tower and replacement therewith by a heat exchangeraccording to the present invention and reconnection of the fluidconduits.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1-21. (canceled)
 22. A fluid cooling heat exchange unit including: aprimary heat exchange unit including a closed circuit for fluid; an aircooler located upstream of said primary heat exchange unit; and a fanarrangement operable to force air through said air cooler and saidprimary heat exchange unit, wherein said air cooler includes a moistureabsorbent material that is, in use, maintained moist such that airforced through said air cooler is cooled by the action of evaporationprior to being forced over a portion of the closed circuit in theprimary heat exchange unit.
 23. A fluid cooling heat exchange unitaccording to claim 22 including a plurality of air inlets and outletswith the fan arrangement disposed therebetween and operable to draw airin through the plurality of inlets and force air out through theplurality of outlets.
 24. A fluid cooling heat exchange unit accordingto claim 23 wherein a plurality of air coolers are located over saidplurality of air inlets such that air drawn through said air coolers bythe fan arrangement is cooled prior to being drawn or forced over theprimary heat exchanger, the air subsequently being discharged throughthe plurality of air outlets.
 25. A fluid cooling heat exchange unitaccording to claim 22 wherein the fluid passes through the primary heatexchange unit in thermally conductive tubing.
 26. fluid cooling heatexchange unit according to claim 22 wherein the absorbent material ismoistened with water.
 27. A fluid cooling heat exchange unit accordingto claim 26 wherein the water used to moisten the absorbent material isseparate from the fluid to be cooled.
 28. A fluid cooling heat exchangeunit according to claim 22 wherein the moisture absorbent materialincludes a plurality of fluted apertures where the apertures are lessthan 7 mm in diameter.
 29. A fluid cooling heat exchange unit accordingto claim 22 wherein the fluid to be cooled is water.
 30. A fluid coolingheat exchange unit according to claim 22 wherein the cooling fluid isammonia.
 31. A fluid cooling heat exchange unit according to claim 22wherein the cooled air emitted from the air cooler is substantially freeof fluid in a liquid state.
 32. A fluid cooling heat exchange unitaccording to claim 22 wherein the air cooler and the primary heatexchange unit are separated by a distance along the path of air flowfrom the cooler to the primary heat exchange unit to reduce thelikelihood of fluid in a liquid state passing from the air cooler andimpinging upon the primary heat exchange unit.
 33. A water cooling heatexchange unit according to claim 22 wherein the water passes through theprimary heat exchange unit in thermally conductive tubing.
 34. A watercooling heat exchange unit according to claim 22 wherein the absorbentmaterial is moistened with water.
 35. A water cooling heat exchange unitaccording to claim 34 wherein the water used to moisten the absorbentmaterial is separate from the cooling water.
 36. A water cooling heatexchange unit according to claim 22 wherein the cooling water is treatedwith chemicals to prevent corrosion and/or rust of metallic parts.
 37. Amethod of cooling fluid in a fluid cooling heat exchange unit, themethod including the steps of: passing cooling fluid of a cooling systemthrough a primary heat exchanger having a closed fluid circuit such thatthe fluid is contained; placing an air cooler upstream of the primaryheat exchanger; and causing a flow of air through said air cooler andover a portion of the closed fluid circuit wherein said air coolerincludes a moisture absorbent material that is, in use, maintained moistsuch that the air is cooled by vaporising fluid.
 38. A method ofconverting a cooling system incorporating a first heat exchange unitincluding a fluid cooling heat exchange unit where the fluid is exposedto air drawn through the heat exchange unit by replacing said first heatexchange unit with a second heat exchange unit including a primary heatexchanger and an air cooler including a moisture absorbent material thatis, in use, maintained moist such that air forced through the air cooleris cooled by the action of vaporisation where the fluid in the primaryheat exchange unit is contained and prevented from exposure to airforced through the air cooler and then subsequently passed through thesecond heat exchange unit, the method including of steps of:disconnecting the first heat exchange unit cooling fluid inlet andoutlet connection; reconnecting the fluid inlet and outlet to thecorresponding connection points of the second heat exchange unit; andoperating the cooling system.
 39. A cooling system having a fluidcooling heat exchange unit including: a primary heat exchange unitincluding a closed circuit for cooling fluid; an air cooler including amoisture absorbent material that is maintained moist for cooling air byevaporation said air cooler located upstream of said primary heatexchange unit; and a fan arrangement operable to force air through saidair cooler and said primary heat exchange unit, wherein air forcedthrough said air cooler is cooled prior to being forced over a portionof said closed circuit in said primary heat exchange unit.
 40. A coolingsystem having a fluid cooling heat exchange unit including: a primaryheat exchange unit including a closed circuit for circulating fluid; anda secondary heat exchange unit including a moisture absorbent materialthat is, in use, maintained moist, the secondary heat exchange unitadapted to provide air cooled by the action of evaporation incommunication with said primary heat exchange unit.
 41. A water coolingheat exchange unit including: a primary heat exchange unit including aclosed circuit for containing cooling water; an air cooler locatedupstream of said primary heat exchange unit; and a fan arrangementoperable to force air through said air cooler and said primary heatexchange unit, wherein said air cooler includes a moisture absorbentmaterial that is, in use, maintained moist such that air forced throughsaid air cooler is cooled by the action of evaporation prior to beingforced over a portion of the closed circuit in the primary heat exchangeunit thus cooling the water contained therein.
 42. A water cooling heatexchange unit according to claim 41 including a plurality of air inletsand outlets with the fan arrangement disposed therebetween and operableto draw air in through the plurality of inlets and force air out throughthe plurality of outlets.
 43. A water cooling heat exchange unitaccording to claim 42 wherein a plurality of air coolers are locatedover said plurality of air inlets such that air drawn through said aircoolers by the fan arrangement is cooled prior to being drawn or forcedover the primary heat exchanger, the air subsequently being dischargedthrough the plurality of air outlets.
 44. A method of cooling water in awater cooling heat exchange unit, the method including the steps of:passing cooling water of a cooling system through a primary heatexchanger having a closed water circuit such that the water iscontained; placing an air cooler upstream of the primary heat exchanger;and causing a flow of air through said air cooler and over a portion ofthe closed water circuit wherein said air cooler includes a moistureabsorbent material that is, in use, maintained moist such that the airis cooled by vaporising the fluid.
 45. A method of converting a coolingsystem incorporating a first heat exchange unit including a watercooling heat exchange unit where the water is exposed to air drawnthrough the heat exchange unit by replacing said first heat exchangeunit with a second heat exchange unit including a primary heat exchangerand an air cooler including a moisture absorbent material that is, inuse, maintained moist such that air forced through the air cooler iscooled by the action of vaporisation where the water in the primary heatexchange unit is contained and prevented from exposure to air forcedthrough the air cooler and then subsequently passed through the secondheat exchange unit, the method including of steps of: disconnecting thefirst heat exchange unit cooling water inlet and outlet connection;reconnecting the water inlet and outlet to the corresponding connectionpoints of the second heat exchange unit; and operating the coolingsystem.
 46. A cooling system having a water cooling heat exchange unitincluding: a primary heat exchange unit including a closed circuit forcooling water; an air cooler including a moisture absorbent materialthat is maintained moist for cooling air by evaporation said air coolerlocated upstream of said primary heat exchange unit; and a fanarrangement operable to force air through said air cooler and saidprimary heat exchange unit, wherein air forced through said air cooleris cooled prior to being forced over a portion of said closed circuit insaid primary heat exchange unit.
 47. A cooling system having a watercooling heat exchange unit including: a primary heat exchange unitincluding a closed circuit for circulating water; and a secondary heatexchange unit including a moisture absorbent material that is, in use,maintained moist, the secondary heat exchange unit adapted to provideair cooled by the action of evaporation in communication with saidprimary heat exchange unit.